1. Field of the Invention
This invention relates to a diaphragm-type valve and more particularly to a flexible metal diaphragm-type valve having a valve stem that extends through the flexible metal diaphragm and is rigidly connected to the valve disc assembly.
2. Description of the Prior Art
Diaphragm-type valves as disclosed in U.S. Pat. Nos. 2,983,480 and 2,812,777 include a valve stem arranged for reciprocal movement within the chamber of a valve body. The valve stem has a lower end portion abutting the top surface of a diaphragm assembly. Axial movement of the valve stem is transmitted through the diaphragm which seals the lower portion of the valve chamber from the upper portion of the valve chamber. A valve member is reciprocally positioned in the chamber in overlying relation with the valve seat to move between a position spaced from the valve seat and a position abutting the valve seat. A cap of the valve member abuts the bottom surface of the diaphragm.
A spring, as disclosed in U.S. Pat. No. 3,982,729, is positioned around the valve member and abuts at one end a cup shaped member movably positioned within the lower portion of the valve chamber and at the other end to the upper portion of the valve member. With this arrangement the spring urges the valve member toward an open position. Downward movement of the valve stem is transmitted through the diaphragm assembly to the upper portion of the valve member. The force transmitted through the diaphragm to the valve member overcomes the force of the return spring to urge the valve member into abutting and sealing relation with the valve seat to close the valve.
For valves of the above type which are utilized to control the flow of contaminated fluids as encountered in nuclear power plants and the like, it is of prime importance that the valve be operable to maintain the valve member in a preselected position, i.e., opened or closed or in a position therebetween. A problem of a valve malfunction occurs as a result of throttling of the line fluid resulting in the valve member bouncing or rotating causing damage to the valve member. Damage of the valve member also occurs for a valve having a large number of internal parts due to vibration imparted to the valve parts. For example, vibration of the return spring can result in damage to the valve member. If the vibration becomes excessive, the effectiveness of the valve to seal the inlet from the outlet is substantially impaired.
Other difficulties encountered with conventional diaphragm-type valves include the inoperability of valves to operate bidirectional, i.e. to control the fluid flow in both directions through the valve. This is particularly the case with a normally unidirectionally operated valve which is inoperable to effect valve opening during backflow. With many valves utilizing an automatic operator to control fluid flow it is difficult to provide the required thrust to (1) maintain the valve disc on the valve seat without leakage and (2) overcome the pressure across the valve seat to effect valve closure. Also, there are occasions in the operation of a unidirectionally operated valve to cause a differential pressure across the valve seat thereby requiring that the valve disc be moved from the valve seat with high pressure over the valve seat. Spring biased diaphragm-type valves are unsuitable for this operation. Furthermore, spring biased diaphragm valves are not satisfactory for use in petro-chemical plants to control the flow of highly viscose fluids or slurries because of the increased surface areas provided in the valve for the collection of foreign matter which interferes with the operation of the valve. In addition spring biased diaphragm valves are inefficient to maintain the valve disc locked in an intermediate position.
Valve assemblies as disclosed by U.S. Pat. Nos. 2,856,151; 2,880,620; 3,257,095; 3,826,465 and British Pat. No. 1,181,374 provide for direct connection of the valve member to the valve stem. With this arrangement movement of the valve stem raises and lowers the valve member to open and close the valve. Standard gate valves also utilize a direct connection of the valve member to the valve stem.
U.S. Pat. No. 2,638,307 discloses a diaphragm valve having a valve stem threaded into engagement with the internal threaded bore of a ram that is slidable within the valve chamber. The lower end of the ram includes an axial bore through which a screw extends and passes through a bushing of a flexible elastomer diaphragm into threaded engagement with the valve member. With this arrangement the valve member and the ram are connected. The ram and valve member have opposing faces which abut the upper and lower surfaces of the diaphragm. Rotation of the valve stem through a handwheel urges the ram to move downwardly within the valve housing. Downward movement of the ram is transmitted by the screw to the valve member, so that the valve member is moved into engagement with the valve seat to close the valve.
U.S. Pat. Nos. 2,699,801 and 3,838,707 also disclose elastomer diaphragm valves in which the valve stem extends through an aperture of the diaphragm. An elastomer diaphragm is subject to rupture if flexed beyond its elastic limits. Consequently the upper and lower surfaces must be supported to prevent flexing of the diaphragm beyond its elastic limit. As disclosed for the above elastomer diaphragm valves, members such as flanges, cups, discs and the like clamp the diaphragm and support its opposite surfaces to prevent rupture of the diaphragm. These elements add substantial complexity to the internal valve construction.
There is need for a flexible metal diaphragm-type valve having a stable internal construction that is resistant to vibration in order to prevent malfunction of the valve without undue complexity to assure valve operability. Further, there is need for a diaphragm valve operable bidirectionally and capable of precisely controlling fluid flow in an intermediate position between the opened and closed position.